This invention relates to a rock bolt installation tool for use in the installation of a rock bolt assembly into a predrilled rock hole.
In a typical rock bolt installation, a leading end of a rock bolt is at least partially inserted into a rock hole and a trailing end of the rock bolt is engaged with a complementary formation on installation equipment, such as a drill rig, jackleg drill or bolter (hereinafter referred to as a drill rig), in order to install the rock bolt in the rock hole.
To increase stability and to ensure that the rock bolt is maintained in axial alignment with the rock hole, the drill rig is often provided with a prop which engages with a face of the rock mass, into which the rock bolt is to be inserted, and onto which several guide rings are engaged, longitudinally spaced. It is through these rings that the rock bolt passes to guide the bolt into the hole without bending. Often, these guide rigs are removed from the drill rig to remove interference with the passage of a rock bolt with an associated faceplate or the like. Without these guiding formations, the percussive force of the drill rig concentrated on the trailing end of the rock bolt causes the rock bolt to bend during insertion which compromises the rock bolt installation.
A further problem arises when a load indicator is included in the rock bolt assembly, interposed between the nut and spherical seat.
During mechanised installation, the load indicator is pushed against a spherical seat which, in turn, is forced against a faceplate, when the faceplate bottoms out against the rock wall. An operator of the drill rig cannot avoid such a situation as he cannot judge or accurately control the installation depth of the bolt. He will continue to drive the bolt into the hole until the bolt stops moving forwardly.
As a result, the load indicator will be progressively squashed between a trailing formation, such as a nut, and the spherical seat which action can cause premature collapse of the spherical seat as a result of the percussive force of installation rather than a rotationally applied pre-tensioning force. The collapse of the load indicator in this manner results in a false indication that the rock bolt has been sufficiently pretensioned.
The invention at least partially sources the aforementioned problem.